To meet the demand for wireless data traffic having increased since deployment of 4G communication systems, efforts have been made to develop an improved 5G or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post LTE System’. The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems. In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation and the like. In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.
The Internet, which is a human centered connectivity network where humans generate and consume information, is now evolving to the Internet of Things (IoT) where distributed entities, such as things, exchange and process information without human intervention. The Internet of Everything (IoE), which is a combination of the IoT technology and the Big Data processing technology through connection with a cloud server, has emerged. As technology elements, such as “sensing technology”, “wired/wireless communication and network infrastructure”, “service interface technology”, and “Security technology” have been demanded for IoT implementation, a sensor network, a Machine-to-Machine (M2M) communication, Machine Type Communication (MTC), and so forth have been recently researched. Such an IoT environment may provide intelligent Internet technology services that create a new value to human life by collecting and analyzing data generated among connected things. IoT may be applied to a variety of fields including smart home, smart building, smart city, smart car or connected cars, smart grid, health care, smart appliances and advanced medical services through convergence and combination between existing Information Technology (IT) and various industrial applications.
In line with this, various attempts have been made to apply 5G communication systems to IoT networks. For example, technologies such as a sensor network, Machine Type Communication (MTC), and Machine-to-Machine (M2M) communication may be implemented by beamforming, MIMO, and array antennas. Application of a cloud Radio Access Network (RAN) as the above-described Big Data processing technology may also be considered to be as an example of convergence between the 5G technology and the IoT technology.
The 3rd generation partnership project (3GPP) in charge of a cellular mobile communication standard named a new core network architecture a 5G core (5GC) and has been conducting standardization for evolution from the conventional 4G LTE system to the 5G system.
The 5GC supports differentiated functions as follows from an evolved packet core (EPC) which is a network core for the conventional LTE. First, a network slice function is employed. As requirements for the 5G, the 5GC needs to support various types of terminals and services, for example, enhanced mobile broadband (eMBB), ultra reliable low latency communications (URLLC), and massive machine type communications (mMTC). The terminals/services each have different requirements for the core network. For example, the eMBB service will require high data rate, and the URLLC service will require high stability and low latency. Network slicing is a technology suggested to satisfy various requirements of the services. The network slicing is a method of virtualizing one physical network to make multiple logical networks, in which each network slice instance (NSI) may have different characteristics. This becomes possible as each NSI has a network function (NF) fitting characteristics thereof. Various 5G services may be efficiently supported by allocating an NSI fitting characteristics of a service required by each terminal. Second, it is easy to support a paradigm of network virtualization through separation of a mobility management function and a session management function. In the conventional 4G LTE, all terminals may be provided with services from a network through signaling exchange with a mobility management entity (MME) which is single core equipment in charge of registration, authentication, mobility management and session management functions. However, in 5G, in accordance with an explosive increase in the number of terminals, and subdivision of mobility and traffic/session characteristics to be supported according to a type of terminal, when single equipment such as the MME supports all functions, scalability for adding an entity for each function as needed cannot but deteriorate. Therefore, various functions have been developed based on a structure of separating the mobility management function and the session management function for improving scalability in terms of function/implementation complexity of core equipment in charge of the control plane and signaling loads. FIG. 1 shows a network architecture for the 5G system. An access and mobility management function (AMF) managing mobility of a terminal and network registration and a session management function (SMF) managing an end-to-end session are separated from each other, and may transmit and receive signaling to and from each other through an N11 interface. Third, a service and session continuity (SSC) mode is employed in order to support various requirements for continuity of applications or services of a terminal, and an SSC mode may be designated and used for each PDU session. There are three SSC modes. An SSC mode 1 is a mode in which an anchor UPF which is a communication contact point with an external data network (DN) is not relocated while a corresponding session is maintained, even when a terminal moves, and since an IP address (prefix) allocated to the corresponding session is not changed, session continuity at the IP level may be secured. Whereas, SSC modes 2 and 3 allow the relocation of the anchor UPF described above. A difference between the SSC mode 2 and the SSC mode 3 is that in the SSC mode 2, when relocating the anchor UPF, connection with a new anchor UPF needs to be configured immediately after disconnecting connection with an existing anchor UPF, and in the SSC mode 3, the connection with the existing anchor UPF may be maintained while the connection with the new anchor UPF is configured. Therefore, in a session of the SSC mode 3, data transmission may be performed simultaneously through a plurality of anchor UPFs with respect to the same external data network (make-before-break type). However, in a session of the SSC mode 2, since a break-before-make scheme is used, overhead for signaling between entities and tunnel management is small in the core network, but when the anchor UPF is relocated at a point in time at which traffic of a terminal is transmitted, service interruption may occur.